Although the issues can be complex, such events are among the more straightforward issues for a government scientific adviser: there are willing recipients of the advice and the challenge is to collate the evidence and present it in the most effective way.

What is more difficult is ensuring that science is brought to bear effectively on the questions that policymakers know matter but which don't present a single decision moment, or where it is less obvious that science can help. These include "wicked problems" that cross departments, cross disciplines and have timescales longer than the lifetimes of governments. Obesity, mental health and flood risk are examples.

This is the challenge in the role of the government chief scientific adviser: to ensure that the best science and engineering advice is brought to bear effectively on all government policy and decision-making. It requires navigating strategic long-term advice on the one hand and the responsive marshalling of evidence for immediate questions on the other.

Foresight is perhaps the most high profile and sustained programme to draw government attention to what science has to tell us about long-term challenges. Foresight projects aim to provide new research where it is most needed, giving policymakers clear and accessible advice, helping them to keep pace with technological change, and creating links across departments and across disciplines.

To give one example, for the Foresight project on Migration and Global Environmental Change, we brought together around 350 leading experts and stakeholders from 30 countries to look 50 years into the future. We examined how profound changes in environmental conditions such as flooding, drought and rising sea levels will influence and interact with patterns of global human migration. The report revealed that we have so far underestimated the major challenges associated with migration in the context of environmental change and that millions will be "trapped" in vulnerable areas and unable to move, particularly in low income countries.

Whereas Foresight projects each take one to two years to publication and engage with several hundred academics and experts over that time, much advice has to be provided much more rapidly. On a timescale of three to nine months, I introduced the "Blackett" reviews, named after Patrick Blackett, the physicist and one of the founders of operational research. These typically tackle a more immediate challenge, often in the security or defence arena.

Sometimes, of course, the challenge is so immediate that we have minutes or hours to provide advice. During pandemics, the disruption to air travel caused by volcanic ash, and the emergency at Fukushima Dai-Ichi after the tsunami, I have relied on the immediate advice of small groups of experts forming the Scientific Advisory Group for Emergencies (SAGE). SAGE reports to the Cabinet Office Briefing Room (COBR) committee, chaired by the prime minister. We have linked these experiences with the increasingly strong use of science as part of risk-based assessments underpinning the National Risk Register.

Between them, the CSAs have expertise in physical, life and social sciences, and engineering. They bring senior academic, business and Whitehall experience to the table. None of them has exactly the same role. What they each do reflects the scientific and policy needs of their department, along with its structure, history and provision of all forms of analysis.

It is a network that is greater than the sum of its parts. Meeting regularly, CSAs have been able rapidly to exchange the latest intelligence, provide deep specialist science and engineering expertise and provide advice and impromptu problem-solving support to each other. Over the last few months alone, they will have discussed subjects as varied as ash die-back, growing threats from antibiotic resistance, the implications of the West Coast rail franchise affair, and how the UK can benefit financially from the science of the sea floor.

Many leading scientists also work in or closely with business. As the government's chief scientific adviser (GCSA), I have had the privilege of co-chairing the prime minister's Council for Science and Technology, which now includes more senior representatives from R&D-intensive businesses such as Rolls Royce and IBM. Drawing on this academic and private sector membership, the CST has presented on the science of genomics to the PM and contributed strongly to the development of the Life Sciences Strategy.

Dialogue with the national academies has also reached a new level. Last year's joint report by the Royal Society and Royal Academy of Engineering on the risks associated with hydraulic fracturing to access shale gas illustrates how a relatively rapid response by the academies to a well posed question can directly inform government decision-making.

Sometimes it is not enough to consider issues and take action in the UK in isolation. I'd like to see the benefits of science advisers networking in the UK extended much more strongly abroad. A small number of other countries have a GCSA-equivalent, most notably the USA but also Australia, the Czech Republic, India and Latvia, for example. Last year the EU, after many years of deliberation, appointed Professor Anne Glover to the role of European Commission CSA.

Many other countries have mature and independent science advisory systems that are not based on a single GCSA-type role. Clearly, each country has to develop a model that works with the grain of its unique political and academic system. But it will help to ensure that we all get the best value from science advice if it becomes easier for scientists to work together across boundaries. Sometimes it helps just knowing who to call in a crisis.

CSAs depend on a wide range of scientists and engineers working at every level in the public sector. When I arrived in post one of my biggest surprises was that, although I was formally head of the science and engineering profession, no one knew how many scientists and engineers were actually working in government departments. Whitehall doesn't collect information like that. So I invited scientists and engineers to step forward and form the Government Science & Engineering community. From a standing start, we now have over 3,500 members.

During the past year, I have led a group including representatives from the policy and analytical profession, the unions and professional bodies, to review what government will need from that profession in the future. The review shows scientists and engineers come from a huge range of disciplines, work across all areas of the civil service, and are proud to be doing so. Some 91% of the thousands surveyed for the review were positive about declaring themselves to be scientists or engineers, and 61% felt influential in their current role.

Open policymaking is still a fluid term, but it creates opportunities to further strengthen the provision of good science in government. On a daily basis, members of the Government Science & Engineering community are working with those who develop and deliver policy to ask questions, to be curious and innovative. They develop networks that reach into academic, NGO and business communities. They know how to call on these networks at a few hours' notice, and how to engineer new insights and solutions to complex issues over the longer term.

The key point, and a fitting one to conclude on as I leave government, is that ensuring government is properly informed by science is something that all scientists should be involved in. The role of a government scientific adviser, whether on long-term issues or in a crisis, is to act as a conduit of advice rather than a single expert opinion. It is that ability to draw on the ever-developing knowledge of the wider scientific community that ensures the best advice possible is brought to bear.

Professor Sir John Beddington CMG FRS was the UK government chief scientific adviser from 2008 to 2013. He is on Twitter @SirJBeddington. This article is an extract of his contribution to the book Future Directions for Scientific Advice in Whitehall (edited by Robert Doubleday and James Wilsdon) which will be free to download here from 18 April 2013